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PART
2:
Various Applications
This Part
of
the
Manual
provides
essential
information on
how
OPTIMOD-TV
fits
in
with the
rest of
the
equipment
at
your
station.
Studio/Transmitter
Links:
There
are
five
types
of
studio/transmitter
links
(STL's)
in
common
use
internationally
in
TV
audio
service,
whether
single-
or
multi-
channel.
These
are:
1)
Analog
land-lines
(telephone
lines);
2)
50-15,000
Hz
microwave STL's
(single or dual);
3)
Composite baseband microwave STL's
(stereo
service);
4)
Composite
video/audio
microwave
STL's; and
5)
PCM
(Pulse-Code Modulation)
links.
All
except
(3)
carry the audio
either directly or
in
some encoded form
other
than
the
stereo
baseband
to
be
found
in
TV
multiplex stereo service (once
approved).
These
links
are ordinarily fed audio
in
non-encoded
form, and
their
receiver output
is
audio.
In
the case
of
(4),
the audio
in
placed on an
FM
subcarrier
above
the
video baseband.
The
composite
STL
(3)
carries
the
multiplexed stereo baseband,
and
is
therefore
fed from
the output
of a
stereo generator.
The
receiver output
of
the
composite
STL
is
the stereo
baseband
signal,
which
is
applied directly to
wideband
input of
the
TV
transmitter's
aural exciter.
In
general,
highest quality
is
obtained by
use
of a
composite
microwave
STL
(3)
or
video/audio microwave
STL
(4)
provided
that
a
line-of-sight
transmission path
of
less
than 10
miles
or
so exists
between
studio
and
transmitter.
If
not,
RF
signal-
to-noise
ratio,
multipath
distortion,
and
diffraction effects
can cause
serious quality
problems.
The
50-15,
000Hz microwave
system
(2)
provides
more
noise
immunity
than
composite
systems.
However, problems
include gain-
and phase-matching
of
the
left
and
right
channels
in
stereo
service,
preemphasis-induced
overloads,
and
a
requirement
that
the audio applied
to
the
microwave
transmitters
be processed
to
prevent
their
overmodulation.
Land-line
(1)
quality
is
extremely
variable,
ranging
from
excellent
to
atrocious.
The
decision
on
whether
to
employ
land-lines
depends
a
great
deal
on the
line
quality
locally
available.
However,
even
the
best
land-lines
tend
to
slightly
veil
audio
quality
due
to
line
equalizer
characteristics,
phase
shifts,
and
repeaters
of
indifferent quality.
PCM
links
(5)
are
generally unavailable
in
the
USA
as
of
this
writing,
although
they
are
widely
used
in
Europe.
They
achieve good
noise
performance and
consistency
at
the
expense
of a
very sharp high-frequency
cutoff,
rapid
changes
in
group
delay
around
cutoff
(unless
elaborate
phase
equalization
is
used),
and
quantization
distortion.
At
the
moment,
there
is
considerable
disagreement
over
how
elaborate
the coding
must
be
to
render quantization
distortion inaudible to critical
listeners,
and no
PCM
system
should be
accepted without
critical
listening
tests.
OPTIMOD-TV
is
available
in
either single- or dual-chassis configurations.
The
dual-
chassis
splits
the
system
at
a
point
between
the
output
of
the
Dual-Band
Compressor
and
the input of the high-frequency Limiter.
2-1
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